Abstract In a lifestyle modification program, contact with an interventionist (e.g., weight loss coach) creates a sense of supportive accountability that can facilitate behavior change and weight loss. Sustaining a strong sense of supportive accountability after face-to-face intervention contact ends has the potential to improve outcomes during the notoriously difficult weight loss maintenance period. One innovative way of facilitating supportive accountability is providing participants with digital tools that objectively measure weight and PA and track food intake in real-time, making the data from those tools automatically and continuously available to coaches, and designing the timing and content of intervention contacts such that they are responsive to the shared data. Although tools that allow for data sharing from sensors and Internet-based applications are readily available, the ways in which they are integrated into intervention contacts in a lifestyle modification program are not yet optimized, and research has not systematically evaluated the effect of data sharing on behavior. Overweight and obese participants (n = 90) will be recruited from the community for a small RCT in order to test the feasibility, acceptability, efficacy, and mechanisms of action of a lifestyle modification intervention enhanced with data sharing. In weeks 1-12 of the program (i.e., Phase I), all participants will attend 12 weekly, face-to- face, group-based behavioral treatment sessions to induce weight loss. Participants will be provided with a wireless body weight scale, PA sensor, and digital food record app and instructed to use them daily use for self-monitoring purposes. In Phase II (weeks 13-52), participants will be randomly assigned to the standard (LM) or enhanced version of remote lifestyle modification (LM+SHARE). Neither condition will have face-to- face intervention contact during Phase II; remote intervention contact will consist of brief phone calls and text messages provided by the participant's coach. Participants in both conditions will be prescribed continued daily use of the three self-monitoring devices. In the standard LM condition, no digital data from these devices will be directly shared with coaches; intervention encounters will be informed only by the infrequent, delayed self- report of participants (which is the current standard of long-term obesity care), and timing of text messages will be fixed. In LM+SHARE, the digital tools will automatically and continuously transmit body weight, PA, and food record data to the coach. In LM+SHARE, supportive accountability will be enhanced in three ways: 1) participants will receive automated alerts after coaches view their data, 2) timing of personalized text messages from coaches will be responsive to clinically notable change in weight, PA, calorie intake, or use of scale, PA sensor, or food record tool, and 3) content of the text messages and phone calls will be informed by the digital data the coach has viewed, as well as the expectation that the coach will continue viewing data in order to provide ongoing support. Assessments will be completed at 0, 12, 26, 40, and 52 weeks.